Stump cutting machines are well known for removing undesirable tree stumps. Such machines include a rotating cutter wheel driven by a gas or diesel engine. The cutter wheel, while rotating, is advanced toward the stump and laterally across the face of the stump. The cutter wheel is mounted at one end of a boom which is, in turn, pivotally mounted on a support frame. Hydraulic boom swing cylinders are used to pivot the boom about the pivot point to move the cutter wheel back and forth across the face of the stump to cut it away.
Stump cutters are often subjected to overload conditions which result in premature failure of certain components such as structural and shielding members, engines and drive train members. Also, with most engines, a loss of power output occurs during an overload condition as the engine speed is reduced below a rated operating speed. Less power to the curing wheel results in reduced productivity. Further, the loss of cutter wheel speed causes a loss of cutter wheel energy which results in the wheel being less effective in smoothing out shock loads. Such loads may be several times greater than the maximum engine output torque. Also, when the cutter wheel loses speed, engine power required to accelerate the wheel back to full speed is not available for curing the stump.
In prior art stump cutting machines, an operator has access to a needle valve to permit the operator, at his discretion, to adjust the needle valve to control the hydraulic oil to the boom cylinders in order to properly load the engine. The operator commonly adjusts the needle valve based on the sound of the engine. Such an adjustment is subject to operator error. Furthermore, an operator may not react fast enough or frequently enough to adapt to changing engine load conditions. Also, an operator might simply forget to adjust the needle valve or otherwise fail to adjust the valve during operation. As a result, at any given moment, the engine may be either overworked or underworked.
Those concerned with these and other problems recognize the need for an improved feed rate control system for stump cutters.